The invention described herein pertains to supporting grids for a gnomon in a sundial structure and addresses the problem of shadow interference—i.e., shadow obstruction of a gnomon shadow by shadows of a supporting grid (e.g., a hemispheric armillary with arcuate arms along the spherical virtual surface tied to crossing rings to form the grid). During the course of the day, shadows of the arms of the armillary hemisphere will align with the gnomon in relation to the sun and eclipse the gnomon shadow completely, making it difficult at such intervals to tell the time.